Papers by Keyword: X-Ray Diffraction (XRD)

Abstract: Al-pillared montmorillonites (Al-MMT) were synthesized from naturally occurring sodium montmorillonite through exchange of interlamellar ions with hydroxyalumina polycations. Furthermore, Powder X-ray diffraction (XRD), Fourier transformation infra-red spectra (FTIR), Thermogravimetric analysis (TG), and differential scanning calorimetry (DSC) were applied in order to study the themal stability, hydrothermal stability and synthesis mechanisms of pillared materials. The Al-MMT are thermally stable and hydrothermal stability up to700°C. X-ray diffractograms of Al-MMT calcined at 700 0C show a sharp and intense d001 peak, corresponding to a basal spacing of 1.66nm. Until calcinations at 8000C, the pillared clays generally retain their structural ordering as evidenced by a broad basal (001) peak, which is an indication that the layer structure lost some long-range ordering. In a 100% steam flow under atmospheric pressure at 7000C, the characteristic d001 spacing of Al-MMT decreases from 1.83nm to 1.71nm, intensity of basal peak reduced by58%. However, after hydrothermal at 8000C, the basal (001) peak is not observed, indicating a complete structural collapse. Synthesis mechanisms for Al-MMT are established. Some of tetrahedral silicons or aluminums inverse towards gallery to react with pillaring agents and yield Alp-O-AlsⅣ or Alp-O-Sis bridges which would firmly fix the pillars to the host clay.

Abstract: A nanostructured powder with uniform distribution of Ni and Cu powders was produced by means of the Ball Mechanical Alloying Treatment (BMAT). Mutual diffusion of Ni and Cu in the nanostructured layer and the microstructure of the cross section of the remaining powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Electron Probe Microanalyzer (EPMA). X-ray diffraction patterns revealed that increasing the milling time gives rise to decreasing crystallite size and lattice parameter during the MA process. Furthermore, scanning electron microscopy (SEM) was utilized not only for evaluating the morphology and microstructure of the remaining powder particles but also for proving this claim that during MA process, the mutual diffusion of Ni and Cu has occurred. Elemental mappings also show that the alloying process occurred in samples but obtaining the uniform shape, size and microstructure of the powder requires increase in the milling time.

Abstract: A method for synthesizing carbon-encapsulated metal nanoparticles(CEMNPs) is reported. In the proposed method, a composite precursors containing various nitrate dissolved in absolute ethanol is ignited by a nonelectric detonator in nitrogen gas in an explosion vessel. Upon the completion of detonation reaction, CEMNPs (Fe@C, Ni@C, Co@C) with diameters ranging from a few nanometers to about 20 nm are produced in the explosion vessel.The material characteristics of these nanoparticles are then examined with the XRD, TEM, EDX and VSM, which characterize the feature of morphology, components, phases and magnetism of nano-composite particles. The composite particles whose coating shell were graphite carbon could be dispersed finely. The core of nanoparticles were composed of iron,cobalt and nickel crystal to that of the above explosive precursors.The magnetic analysis indicated that the different composite nanoparticles have good ferromagnetism and superparamagetism in room temperature.

Abstract: In order to meet the requirements of growing high-quality ZnGeP2, a crystal growth furnace with three-temperature-zone was designed and fabricated based on a conventional vertical two-zone tubular resistance furnace. Appropriate temperature gradients of 12~15°C/cm at the growth interface and stable thermal profile were obtained. A crack-free ZnGeP2 single crystal with size of Φ15mm×30mm was grown successfully in the furnace mentioned above. The as-grown crystal was characterized by X-ray diffraction (XRD) and Infrared (IR) spectrophotometers. It is found that there is a cleavage face of (101) and X-ray multiple diffraction peaks of the {101} faces are observed, The infrared transmission of a ZnGeP2 wafer of 3 mm thickness is about 50% in the region of 3~10μm. These results show the designed crystal growth furnace is suitable for growth of ZnGeP2 crystal, and the as-grown ZnGeP2 crystal has good structural integrity and high quality.

Abstract: Tin oxide material (SnO2) is synthesized in nano scale range and is characterized. The refined X-ray intensity data was obtained from the Reitveld method. The electron density of nano SnO2 is determined using MEM (Maximum Entropy Method). Using one, two and three dimensional MEM maps, the bonding within the atoms is clearly understood. The particle size of SnO2 is also analyzed using XRD and SEM.

Abstract: Cement-in-polymer (c/p) dispersions allow the full utilisation of the reinforcing abilities of multifilament rovings in concrete. In this work the role of the polymer properties on the performance of the c/p dispersions is investigated and discussed. Two model polymers are chosen and c/p dispersions made with these are investigated regarding the water ingress velocity (NMR), the phase development during cement hydration (XRD), and the microstructure after cement hydration (SEM). Best mechanical performance is achieved with the hydrophobic poly(vinyl acetate) which regulates the water ingress and causes a slow hydration of the cement.

Abstract: Hydration of cement in the presence of SBR dispersion and powder respectively was investigated using the methods of ITC, XRD and ESEM. The results show that both the dispersion and powder of SBR facilitate the formation, enhance the stability of AFt and inhibit the formation of C4AH13 in cement paste; the effect of the powder is more evident than the dispersion. Both the dispersion and powder of SBR delay the formation of C-S-H and Ca(OH)2 in cement paste, and the effect of the dispersion is more evident. Up to 3 days, the structure of the SBR dispersion – or powder – modified cement pastes has no significant difference with that of control paste except due to a thin polymer film on the surface. The two polymers delay the early cement hydration, but have no significant effect after 3 days.

Abstract: this paper presents the results of a study in which the combination of two polymeric additives in concrete with the intention of improving its mechanical and durability performance is analysed. The additives are a synthetic latex and a biopolymer – chitosan. An evaluation of the mechanical properties as well as the phases formed based on scanning electron microscopy (SEM) and X-ray diffraction (XRD) was performed. The concretes were prepared with each of the polymers separately, and the results were ordinary. However, when combined, the results show an interesting interaction improving the mechanical strengths of the concrete. Several concrete samples were prepared with 0 – 4 % of each polymer with 1 % increments. The mechanical properties were shown to be sensitive to the incorporation of polymers. The desired effect of the interaction between the biopolymer and the latex was observed, because the strengths increased when both additives were present, namely for the combination of 2 % of each polymer. SEM images revealed a heterogeneous distribution in the polymer cementitious matrix, mainly with regards to latex. The presence of well defined polymer fibers on a fracture surface of composites prepared with biopolymer (4 %) was observed, indicating that the fibre pullout and not fracture was the cause of failure, resulting from the poor adherence of the fibers in matrix. Composites prepared with both polymers revealed abundant formation of C-S-H and the absence of ettringite, explaining the improvement of mechanical properties. The presence of reticulated structures of C-S-H dispersed in the microstructure and involving the calcium hydroxide corroborates the results of mechanical properties, mainly for the percentages of 3 % of biopolymer and 1 % of latex.

Abstract: The objective of this study is to improve the sintering of W powder through increasing the density of the crystalline structure imperfections. The powder of W was processed by short processes of mechanical milling in a high energy planetary mill. The paper presents the influence of mechanical milling process duration upon the modifications of the structural characteristics of W powder. The fine structure has been studied by using X-ray diffraction.

Abstract: The paper presents the experimental work regarding the elaboration of some nanocomposite powders with higher SiC content. For the research, three types of mixtures were prepared: 90SiC-10Al, 70SiC-30Al and 60SiC-40Al using mechanical alloying (MA) technique. The MA was carried out in a vario planetary ball mill Pulverisette 4 for 5 hours using different conditions: - the shock mode (the main disk speed 400 rpm and the planets speed -800 rpm); - the friction mode (the main disk speed 400 rpm and the planets speed 800 rpm). The resulting mixtures was investigated by scanning electron microscopie (SEM), X-ray diffraction pattern (RDX), energy dispersive X-ray analysis (EDAX) and particle size distribution. After 5 hours of MA it is observed that the mixture obtained in the friction mode conditions have a homogenous structure and the particle size distribution is better than the particle size distribution of the mixture obtained in the shock mode conditions.